Spectral line width decrease in the solar corona: resonant energy conversion from Alfvén to acoustic waves

Free access article

Issue		A&A Volume 456, Number 3, September IV 2006


Page(s)		L13 - L16
Section		Letters
DOI		http://dx.doi.org/10.1051/0004-6361:20065805

A&A 456, L13-L16 (2006)
DOI: 10.1051/0004-6361:20065805

Letter

Spectral line width decrease in the solar corona: resonant energy conversion from Alfvén to acoustic waves

T. V. Zaqarashvili^{1, 2}, R. Oliver¹ and J. L. Ballester¹

¹ Departament de Física, Universitat de les Illes Balears, 07122 Palma de Mallorca, Spain
e-mail: [temury.zaqarashvili; ramon.oliver; dfsjlb0]@uib.es
² Georgian National Astrophysical Observatory (Abastumani Astrophysical Observatory), Kazbegi Ave. 2a, Tbilisi 0160, Georgia
e-mail: temury@genao.org

(Received 12 June 2006 / Accepted 19 July 2006)

Abstract
Context.Observations reveal an increase with height of the line width of several coronal spectral lines probably caused by outwardly propagating Alfvén waves. However, the spectral line width sometimes shows a sudden decrease at a height ~0.1-0.2 $R_{\odot}$ , where the ratio of sound to Alfvén speeds may approach unity.
Aims.To explain the observed line width reduction in terms of the energy conversion from Alfvén to another type of wave motion.
Methods.Weakly non-linear wave-wave interaction in ideal MHD.
Results.Qualitative analysis shows that the resonant energy conversion from Alfvén to acoustic waves near the region of the corona where the plasma $\beta$ approaches unity may explain the observed spectral line width reduction.

Key words: Sun: corona -- Sun: oscillations

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